1. Field of the Invention
The present invention relates to radiocommunications, especially mobile radiocommunications, such as radiotelephony, and more particularly to a device and a method for controlling and monitoring the power of the signal from a radiocommunications terminal.
2. Description of the Prior Art
When they are operating, radiocommunications terminals emit a certain quantity of energy due to the electromagnetic radiation produced by the antennas of the terminal when communicating with telecommunications network base stations.
During normal use of a terminal, that is to say when the terminal is near the head of the user, and not held away therefrom, as when using headsets known as “hands free kits”, a certain quantity of energy, referred to as the specific absorption rate (SAR), impinges on the user. This quantity of energy, or near field density, is all the greater if the terminal is operating with the maximum power weighting, that is to say at 33 dBm (or 2 watts peak) according to the GSM standard.
For a given terminal design, the SAR is directly proportional to the efficiency of the antenna and to the transmitted power. The efficiency of the antenna cannot be reduced too much as this would degrade the performance of the terminal, in particular when receiving. It is therefore beneficial to vary the power of the terminal within limits set by the standard.
The patent EP 977 304 discloses a device and a method for monitoring the power emitted in certain directions by a terminal including a plurality of antennas by selectively activating or deactivating one or more antennas.
This type of device necessitates the use of a plurality of monodirectional antennas, which leads to high manufacturing costs and non-negligible complexity of implementation.
Moreover, the corresponding method includes a step of detecting human presence in the vicinity of the device whose reliability is somewhat doubtful given the operating constraints of the terminal.
Other prior art methods limit the radiation from the terminal during a maximum period in order to reduce the radiation absorption rate or the mismatching of the antenna and the transmit band.
However, these prior art methods compromise the efficiency of the terminal in operation and the mismatching of an antenna by the prior art method is irreversible. Such mismatches compromise the performance of the antenna when receiving.
Against this background, the present invention alleviates the drawbacks of the prior art by proposing a simple device and a simple method for reducing the quantity of energy impinging on the user of a radiocommunications terminal when sending without compromising its performance when receiving.